The Disney movie Inside Out, portrayed the five basic emotions behind our daily decisions as joy, sadness, anger, fear and disgust. At first, the choice of disgust as a core emotion may be surprising. However, scientific research has shown that disgust serves a vital role in our daily decision making process and protects us from harm 1. In this article, we will explore how disgust functions as our behavioral immune system to defend us from pathogens.
Disgust and Hygiene
The emotion of disgust is experienced by both humans and animals3. Charles Darwin was the first to propose the theory that disgust is universally experienced and since then, other researchers have found data to further support his theory3. Both humans and animals have been shown to have basic hygiene instincts: that is, they have an innate need to avoid objects potentially contaminated with disease4. Just think about how often you wash your hands.
Do you wash your hands after going the bathroom? Blowing your nose? Before eating? Researchers have discovered that hygiene goes back to before germ theory (the idea that disease is caused by microbes, which are too small to see with the naked eye) was established and accepted 4. People engaged in hygienic practices like regularly bathing and grooming even back in the caveman days4. Neanderthals are believed to have carried out grooming with combs and cleaning with soap to remove parasites4. We could learn a thing or two about hygiene from them.
Even though it may seem that hand washing is commonplace nowadays the rates of regular hand washing are a far cry from 100%5. Only 4% of mothers in Madagascar and 12-14% of mothers in China wash their hands after going to the bathroom5. In the UK, 32% of men and 64% of women wash their hands after using the bathroom5. If hand washing with soap was practiced more regularly across the world, it could save over a million lives a year from infectious diseases5.
Disgust: Triggers and Behaviors
Both animals and humans have a behavioral immune system4. Common triggers include bodily wastes like urine or feces; body contents such as blood or vomit; sick, deformed or dead people; spoiled food; and any object that gets contaminated by any of the triggers listed above3. In addition, disgust has a commonly shared facial expression (Figure 2)
Besides making a “yuck face”, disgust involves other actions such as moving away from the trigger, dropping the trigger, shuddering, and nausea3. Studies involving brain imaging when the subjects viewed disgusting pictures revealed that there is a specific network of neurons become active when the person felt disgust3. Disgust has even been shown to activate parts of the immune system such as increasing expression of inflammatory molecules like TNF-α (to alert the immune system of potential invaders) in saliva, provoking a more aggressive immune response through increased levels of the cytokine IL-6 (cytokines act as an alert signal to cells), and increasing the skin's resistance to pathogen invasion by increasing its ability to conduct electrical charge via increased sweat production 6,7. In other words, disgust makes you more likely to avoid pathogens and better prepares you to defend yourself against them. Pathogen avoidance and hygienic practices encouraged by your behavioral immune system is widespread across many cultures3.
While disgust and behavioral immune system actions may be universal, there are variations. People who suffer from obsessive compulsive disorder may experience more extreme sensitivity to disgust triggers, whereas people who suffer from Huntington’s Disease may experience lower amounts of disgust3. Women tend to have greater disgust sensitivity than men, perhaps because the responsibility of raising children often falls to them so they may have increased disgust sensitivity to better protect their children3. In addition, during the first trimester of pregnancy, women tend to have increased disgust sensitivity, getting nauseated more frequently which is more commonly known as morning sickness3. This increased ability to feel disgusted may limit the future mother’s exposure to toxins and pathogens while she and her baby are vulnerable33. To determine your own disgust sensitivity level, there is a survey you can take8. Disgust Survey
As depicted in Disney’s Inside Out movie, disgust is a core emotion that is essential to our lives. Both disgust and hygiene instincts are universal3. When we feel disgusted by something, we take certain actions that serve to protect us from pathogens and subsequent sickness. Disgust also affects the immune system, making it stronger in order to better protect us from pathogen invasion6,7. In addition, disgust and avoidance behaviors are essential to stopping the spread of disease5. Our behavioral immune system evolved to take advantage of disgust to protect us from disease. Disgust helps to keep us healthy.
- Schaller, M. & Park, J. H. The Behavioral Immune System (and Why It Matters). Curr. Dir. Psychol. Sci. 20, 99–103 (2011).
- Curtis, V., de Barra, M. & Aunger, R. Disgust as an adaptive system for disease avoidance behaviour. Philos. Trans. R. Soc. B Biol. Sci. 366, 1320–1320 (2011).
- Curtis, V., de Barra, M. & Aunger, R. Disgust as an adaptive system for disease avoidance behaviour. Philos. Trans. R. Soc. Lond. B. Biol. Sci. 366, 389–401 (2011).
- Curtis, V. A. Dirt, disgust and disease: a natural history of hygiene. J. Epidemiol. Community Health 61, 660–4 (2007).
- Curtis, V. Why disgust matters. Philos. Trans. R. Soc. London B Biol. Sci. 366, (2011).
- Stevenson, R. J., Hodgson, D., Oaten, M. J., Barouei, J. & Case, T. I. The effect of disgust on oral immune function. Psychophysiology 48, 900–907 (2011).
- Schaller, M., Miller, G. E., Gervais, W. M., Yager, S. & Chen, E. Mere Visual Perception of Other People’s Disease Symptoms Facilitates a More Aggressive Immune Response. Psychol. Sci. 21, 649–652 (2010).
- Haidt, Jonathan, McCauly, Clark, Rozin, P. The Disgust Scale Home Page. (2012). at http://people.stern.nyu.edu/jhaidt/disgustscale.html